The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Certain medical devices are used to regulate the flow of fluids and substances in and out of a patient's body. Endotracheal tubes and tracheostomy tubes are two specific examples of such a medical device. These devices, also known as tracheal tubes, assist the patient in breathing and regulate the airflow in and out of the patient's lungs. Endotracheal tubes are inserted through the patient's mouth down into the trachea, whereas tracheostomy tubes are inserted through a surgical incision in the patient's neck. Ventilators are generally attached to the tracheal tubes to assist the patient's breathing.
To ensure proper regulation of air flow and to prevent unwanted fluids or other substances from entering the lungs, a seal between the tracheal wall and the tracheal tube is desirable. With a proper seal, the only passageway into the lungs is through the regulated tracheal tube. This seal is usually achieved through the use of an inflatable cuff attached to the tracheal tube. The cuff is deflated when the device is inserted into the patient's trachea, and, once the tracheal tube is in position, the cuff is inflated to achieve a seal between the inner wall of the trachea and the outer wall of the tracheal tube. The cuffs are generally inflated with air, but other fluids can be used, including liquids. However, inflatable cuffs can cause multiple problems related to maintenance, patient discomfort, and potential medical complications. Thus, elimination of the problems related to current inflatable cuff designs is desirable.
There are two general categories of cuffs: complaint cuffs and noncompliant cuffs. Noncompliant cuffs are made of an inelastic material, typically polyvinyl chloride (PVC), and thus have a set volume when fully inflated. Noncompliant cuffs are inflated at a low pressure, which ensures that the cuff applies a corresponding low pressure against the tracheal wall when fully inflated. Therefore, patients encounter minimal discomfort when noncompliant cuffs are used. However, tracheas vary in size, ranging anywhere from 18 to 25 millimeters in diameter. To further complicate this process, clinicians do not know the diameter of the patient's trachea when performing an endotracheostomy or tracheostomy, thus they typically merely estimate the tracheal diameter based on external characteristics of the patient, such as gender and body type. Because of varying tracheal diameters, noncompliant cuffs are designed to fit any sized trachea. However, this universal cuff design presents problems, especially when a patient with a smaller trachea is presented. With the inelastic material used for noncompliant cuffs, the cuffs must have a fully inflated diameter large enough to seal the largest tracheas. Therefore, with a smaller trachea, a smooth seal is not achieved between the cuff and the tracheal wall because the cuff is not able to fully expand. Instead, cuff folds are formed due to the extra, unused material of the noncompliant cuff. These cuff folds create passageways for bacteria and other unwanted substances to travel around the tracheal tube and reach the lungs. These cuff folds can cause several complications, but the most common issue is ventilator associated pneumonia. Bacteria are able to freely colonize within these cuff folds because the cuff folds shield them from removal and treatment by clinicians. The bacteria then leaks down through the cuff folds into the lungs, causing the patient to contract pneumonia. Thus, elimination of cuff folds is a desirable goal of tracheal tube designs.
To eliminate cuff folds and their associated problems, compliant cuffs can be used. These cuffs are made of an elastic material that can be inflated to a variety of tracheal diameters while maintaining a smooth seal between the cuff and the tracheal wall. The elastic material ensures a proper seal without cuff folds regardless of the tracheal diameter. However, the elastic material is often delicate and prone to tears or leaks. Therefore, the cuff wall of a compliant cuff is usually relatively thick, which then causes the cuff to require a higher pressure to properly inflate it. Additionally, since the clinician does not know the exact size of the given trachea, the cuff is generally inflated to a pressure that ensures that the trachea will be completely sealed regardless of the actual tracheal diameter. This higher pressure, which is exacerbated in patients with smaller tracheas, causes a corresponding amount of pressure to be applied to the tracheal wall. The high pressure can cause patient discomfort and, more seriously, tracheal ischemia and even necrosis. This danger is more severe when the endotracheal or tracheostomy tube is in place for a prolonged period of time. Tracheal ischemia is a restriction in blood supply to the tissues surrounding the cuff which causes a shortage of oxygen and glucose. If ischemia persists for a long period of time, the lack of nutrition will cause necrosis to occur and the tissue will die. The risk of ischemia is greater for tracheostomy tubes, as they are generally more permanent than endotracheal tubes. Therefore, while compliant cuffs create a proper seal against the tracheal wall, elimination of the high pressure on the tracheal wall is desired.
Additionally, both compliant and noncompliant cuffs require regular maintenance to ensure proper continuous inflation. Compliant cuffs are made of highly permeable or semi-permeable materials, meaning the cuff deflates naturally at a high rate as air slowly leaks through the walls of the cuff. Thus, the pressure must be frequently checked to maintain a proper seal between the cuff and the tracheal wall. Even noncompliant cuffs, despite the use of materials with lower permeability such as PVC, still deflate eventually. Clinicians must check the cuff pressure every 4-8 hours to ensure proper continuous inflation. Often, this check is overlooked due to more critical responsibilities requiring the clinicians' attention, causing the complications discussed above to become more frequent and severe. Thus, a cuff that requires less regular maintenance is desirable.